40 THE ACTIVE FORCES OF LIVING ORGANISMS 

 MuscTiiar When a muscle contracts in rigor mortis it will give 



contrac- .,, 



tion is a off a Considerable amount of carbonic acid. It will 



13X00638 of 



deoxida- do this even if placed in a vacuum, after it has been 

 shown by means of a mercurial air-pump to contain 

 no free oxygen.* It is clear, therefore, that the 

 oxygen of the carbonic acid was held in the muscular 

 tissue either in that form or in some more complex 

 body. Since, however, carbonic acid is one of the 

 chief products of muscular contraction, not only in 

 rigor mortis but in the normal state also, there seems 

 to be some ground for supposing the muscular con- 

 traction to be essentially a process depending on a 

 diminution of the supply of oxygen in the tissue. 

 The more perfect the state of oxidation before the 

 contraction takes place, the greater the diminution 

 would naturally be under the influence of a sufficient 

 stimulus. Thus, though perfect oxidation is essential 

 to muscular action, the actual cause of the contraction 

 lies probably, as remarked, in a diminution of the 

 state of oxidation of the tissue taken as a whole. 

 There appear, however, to be reasons for believing 

 muscular tissue to be of a complex nature, and it is 

 likely that one or two only of the various bodies which 

 compose it break up in the contraction, whilst the mole- 

 cules of the other bodies coming under the influence, 

 so to speak, of a wave of diminished oxidation, group 

 themselves in the peculiar manner which constitutes 

 muscular contraction. The production of heat during 

 the contraction can only be attributed in a general 

 * Foster, loc. cit., p. 100. 



